1. Field
The present disclosure relates to a synergistic herbicidal composition containing mesotrione and mesosulfuron-methyl, each in particular crystal modifications. The composition finds use in controlling the growth of undesirable plant, particularly in crops, including using the aforementioned composition.
2. Description of Related Art
The protection of crops from undesirable plant, which inhibits crop growth, is a constantly recurring problem in agriculture. To solve this problem, researchers are trying to produce an extensive variety of chemicals and chemical formulations effective in the control of such undesirable growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use.
Some herbicidal active ingredients have been shown to be more effective when applied in combination rather than applied individually, this effect being referred to as “synergism.” According to Herbicide Handbook of the Weed Science Society of America, Seventh Edition, 1994, page 318, “synergism” is an interaction of two or more factors such that the effect when combined is greater than the predicted effect based on the response to each factor applied separately.
The compound 2-(4-mesyl-2-nitrobenzoyl)cyclohexane-1,3-dione has the common name “mesotrione”. Mesotrione is a substance that can form polymorph crystals. Two different forms, crystalline modifications I and II, of mesotrione are described in WO2006021743, which is incorporated herein by reference for all purposes. Mesotrione is active as a herbicide and is now commercially available in a range of formulations for controlling the growth of undesirable plant.
The compound methyl 2-[(4,6-dimethoxypyrimidin-2-ylcarbamoyl)sulfamoyl]-α-(methanesulfonamido)-p-toluate, having the common name “mesosulfuron-methyl”, is a member of the sulfonylurea group of chemicals. Mesosulfuron-methyl is a potent herbicide having high selectivity, high efficiency, low toxicity and other desirable attributes. It is used post-emergence on crops, such as wheat and cereals, against a variety of annual and perennial grasses and broadleaved weeds. It is rather less toxic towards algae and is of generally low toxicity towards most wildlife.
The commercially available mesosulfuron-methyl, which is usually manufactured by the process described in U.S. Pat. No. 5,648,315, which is incorporated by reference for all purposes, is present in an amorphous state.
It has been found that mesosulfuron-methyl in the amorphous state is highly unstable. It will generally undergo significant hydrolysis when dissolved or dispersed in water. Furthermore, hydrolysis can occur during storage, particularly where the compound is exposed to moisture. It has been found that a crystalline form of mesosulfuron-methyl, termed hereinafter “crystalline modification I”, has an improved stability in formulations (U.S. Ser. No. 14/957,768, filed on even date herewith, and incorporated herein by reference for all purposes. The crystalline modification I of mesosulfuron-methyl of the invention exhibits at least 3 of the following reflexes as 20 values in an X-ray powder diffractogram recorded using Cu-Kα radiation at 25° C.:2θ=5.41±0.2  (1)2θ=10.26±0.2  (2)2θ=10.88±0.2  (3)2θ=12.14±0.2  (4)2θ=16.38±0.2  (5)2θ=18.87±0.2  (6)2θ=19.47±0.2  (7)2θ=20.82±0.2  (8)2θ=21.88±0.2  (9)2θ=22.55±0.2  (10)2θ=22.96±0.2  (11)2θ=23.22±0.2  (12)2θ=24.10±0.2  (13)2θ=24.50±0.2  (14)2θ=26.35±0.2  (15)